I'm still new at official critiques, so bare with me.
Vision-I really like the theme of this piece. I like how I can almost relate to the woman (because everybody's life is shitty at some point), but at the same time, I'm wondering what her story is. Also, loved the pun in the title. Shit. Because she's on a toilet. Ha ha.
Originality-I can't really say this is something I've never seen before, but every thing's been done before, and you don't neccessarly have to do something totally new to be original. I think this has the capacity for a lot more personal style, but I can't call it unoriginal. It's not completely unique, but it has originality.
Technique-This is really well done. The lighting is great, and the model's make up and clothing (or, I guess, lack thereof) fits very well with the theme of the piece. The only thing I suggest changing is the pose. It looks unnatural, and it throws the beauty of the whole piece off.
Impact-This really got my attention, and it stuck with me. It made me want to check out more of your work, so I'd say you've done well in the impact department.